Centrifugal timing switch



May 24, 1960 E. BURRELL CENTRIFUGAL TIMING SWITCH Filed June 2, 1950 umT l a w 1Y4/ 4 3 F M q a w um fl A B a 5 4 a. a

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ATTORNEYS United States Patent CENTRIFUGAL TIMING SWITCH Ellis Bnrrell,Rochester, N.Y., assignor, by mesne assignments, to the United States ofAmerica as represented by the Secretary of the Navy Filed June 2, 1950,Ser. No. 165,977 6 Claims. (Cl. 200-80) This invention relates tocentrifugal unshorting switches.

In one form of centrifugal timing switch of the character described, inRickmeyer 2,435,602 and 2,435,603, a conductive fluid (mercury) is movedby the pressure of centrifugal force to control an electrical circuit.The switch provides a predetermined time delay in opening or closing anelectrical circuit by the flow of the conductive fluid through aplurality of restricted passages in response to centrifugal pressure setup in the switch by the rotation of the mechanism in which the switch ismounted. One important application of this type of switch is in electricfuzes for use in artillery projectiles to remove a short circuit acrossan electrical detonator a desired interval after a projectile is fired.Usually a tubular shell is divided into two compartments by a restriction partition. The conductive fluid (mercury) is confined in onecompartment before the actuation of the switch and the other compartmentacts as a receiver for the fluid. The compartment initially filled withmercury is provided with two electrical contact members insulated fromeach other and electrically communicating with the interior of thecompartment. Usually one contact member is the tubular shell and asecond contact member is mounted in one end of the shell and insulatedfrom it. The mercury bridges the gap between the two confacts tocomplete the electrical circuit through the switch. The restrictionpartition between the two compartments is normally provided withrestricted passages through which the mercury is caused to flow by thepressure of centrifugal force resulting from the spinning of the switch,e.g. during the flight of a projectile. The restricted passages arecapable of preventing the passage of the mercury under the blows andimpacts occurring during normal handling, but upon rotation of theswitch about an axis at one side of the restriction partition,centrifugal pressure will force the conductive fluid through therestricted passages from one compartment into the other. The electricalcircuit is broken when a suflicient volume of mercury has flowed throughthe restricted passages to uncover the end face of the second contactand open the conduction path through the mercury. The time required tobreak the electrical circuit is dependent upon the volume of mercurythat must flow through the restriction partition to uncover the end faceof the second contact and the rate of flow of the mercury through therestricted passages, the latter factor being determined by the pressureagainst the partition due to centrifugal force and the nature of therestricted passages through the restriction partition.

Inherent structural and operational difficulties are present whenmercury is used to make or break an electrical circuit. This conductivefluid often deposits a film of an oxide of mercury across the switchwhich establishes a high resistance short circuit between the contactsafter sufficient mercury has flowed through the restricted passages toopen the electrical circuit. Furthermore, it is extremely diflicult toestablish low resistance contacts with the mercury, and normally aspecial sleeve of coppermx 2,938,089 Patented May 24, 1960 othermaterial having a high afiinity for the mercury must be provided withinthe tubular shell to obtain the desired low resistance contact betweenthe metal shell and the mercury. Similarly, a special ring of coppermust normally be pressed onto the second contact to obtain the desiredcontact resistance with the conductive fluid. Copper has a strongtendency to am-algamate with the mercury causing contamination and theformation of a sludge within the compartment initially filled with theconductive fluid which often adversely affects the flow characteristicof the mercury.

It is an object of the invention to provide a centrifugal unshortingswitch in which a positive short circuit is normally established betweentwo electrical terminals without any possibility of a high resistancebetween the terminals before the electrical circuit is broken.

A further object of the invention is the provision of a centrifugalunshorting switch which eliminates any possibility of the establishmentof a high resistance short circuit between the terminals aftersutficient mercury has flowed through the restriction partition to openthe electrical circuit, and in which it is unnecessary to utilizeelements having a strong tendency to amalgamate with the mercury whichmay cause contamination and the formation of a sludge within the switch.

The invention essentially consists of utilizing a continuous shortingstrip of metal formed with a frangible neck portion instead of relyingupon a conductive fluid to short circuit the contact members, initiallycontaining the mercury within a fixedly positioned, hollowed cylindricalcontainer closed at one end and having a restriction partition sealedacross the open end thereof, and telescoping the container within alight, movable, cupshaped member which normally rests against thefrangible neck portion. Upon rotation about an axis at the side of therestriction partition away from the closed end of the cup-shaped member,the mercury is forced through the restriction partition into the lightcup-shaped mem ber. The pressure of centrifugal force acting upon themercury within the cup-shaped member is exerted against the frangibleneck portion. When a volume of mercury proportional to the required timedelay has flowed through the restriction partition, the pressure ofcentrifugal force breaks the shorting strip at the frangible portion toopen the electrical circuit.

These and other objects, advantages and novel features 10 which may be aspinning projectile or an element power means such as the shaft mountedupon a suitable of a motor. The rotating member 10 is formed with acavity 11 in which a centrifugal unshorting switch 12 is positioned withthe end of the switch through which the terminals 13 protrude closest tothe axis of rotation of the member 10. The invention is particularlyconcerned with the centrifugal switch 12 and the means of breaking theelectrical circuit between the two terminals 13. In rotation of themember 10 centrifugal force will be set up lengthwise of the switch 12in a downward direction as shown in Fig. 2.

. In a preferred embodiment of the invention shown in detail in Figs. 2to 4,a1hollowed inner cup 20 constructed of metal having an extremelylow tendency to amalgamate with mercury, preferably stainless steel, iscounterbored at the open end thereof to form a larger diameter section21 into which two disks 22 and 23 are assembled, and the open end of theinner cup is crimped to clamp the disks 22 and 23 in close contactwithin the larger diameter section 21. The disks 22 and 23 are alsoconstructed of metal having an extremely low tendency to amalgamate withmercury, preferably stainless steel, and the abutting surfaces 24 and 25thereof respectively are roughened by sand blasting or etching asdisclosed in my application Serial No. 165,976 to form a foraminousorifice between the surfaces which prevents the passage of a body ofmercury normally contained within the inner cup 20 at atmosphericpressure under the blows and impacts occurring during normal handlingbut which passes mercury under the pressure of centrifugal force. Aplurality of holes 26 drilled in the top surface of the disk 22 alongthe circumference of a circle concentric with the disk 22 open into anannular distribution groove 27 formed in the roughened face of the disk22. A central hole 28 is provided axially through the disk 23. Theforaminous orifice formed between the abutting surfaces 24 and 25prevents the radial flow of mercury from the annular distribution groove27 thence between these surfaces and out of the hole 28 at atmosphericpressure under the blows and impacts occurring during normal handling.

The end of the inner cup 20 across which the disks 22 and 23 are sealedextends into the open end of a thin larger diameter outer cup 30 totelescope said cups together with the opposite ends thereof closed. Thelight outer cup 30 constructed of suitable insulating material such as aphenolic resin is adapted to slide axially of the inner cup 20 away fromthe axis of rotation of the member 1d in response to the centrifugalforce set up by rotating the switch 12 by means of the member 10.

A thin, narrow shorting strip 31 of suitable metal having a highconductivity such as copper which narrows to a restricted neck portion32 at the center thereof is utilized to effect the desired shortcircuit. A headed member 33 of suitable insulating material such as aphenolic resin is formed with an upwardly extending shank 34 having anindentation 35 hollowed in the end thereof to receive the rounded closedend 36 of the outer cup 30. An annular ring 37 of suitable insulatingmaterial such as a phenolic resin is formed with diametrically oppositevertical grooves 38 and 39 in the inner and outer circumferences thereofrespectively to receive the shorting strip 31. The inner diameter of thering 37 is slightly larger than the diameter of the shank 34, and therestricted neck portion 32 of the shorting strip 31 is stretched tautacross the indentation 35 by placing the shorting strip 31 above theshank 34 and then pressing the ring 37 over the shank 34 with theshorting strip 31 fitting in the grooves 38 until the ring 37 is seatedagainst the head of the member 33. After the ends of the shorting strip31 are bent upward to fit within the grooves 39 in the outercircumference of the ring 37, a tubular sleeve 40 of suitable insulatingmaterial such as a phenolie resin is disposed around the ring 37 andagainst the head of the member 33. The assembled elements are thenpositioned within a steel can 41 with the headed member 33 seatedagainst the closed end 42 of the can 41 and with the ends of theshorting member 31 projecting upwardly toward the open end of the can 41and toward the axis of rotation of the member 10.

A groove 44 is cut in the outer periphery near the closed end of theinner cup 20 to receive a closure washer 45 of suitable insulatingmaterial formed with two diametrically opposite rectangular holes 46through the annulus thereof. When the telescoping inner cup 20 and outercup 30 are assembled within the sleeve 40 with the closed end 36 of theouter cup 30 disposed adjacent the restricted neck portion 32-of theshorting strip 31 and with the closure washer 45 seated against theupper end 47 of the sleeve 40, the vertical arms of the shorting strip31 extend through the rectangular holes 46 in the closure washer 45 andend in soldering terminals 13 to allow external electrical circuitconnections. The edge of the can 41 at the open end thereof is crimpedagainst the closure washer 45 to retain the elements within the can 41.The inner cup 20 and outer cup 30 are in telescoped sliding engagement,but as the washer 45 abuts against the upper edge 47 of the sleeve 40,the inner cup 20 is fixedly positioned and only the outer cup 30 is freeto move away from the axis of rotation of the member 10 in response tothe centrifugal force set up by rotating the switch 12 by means ofmember 10. The shorting strip 31 narrows to a restricted neck portion 32at the center thereof to form a frangible link which can be broken byexerting sufficient pressure against the outer cup 30 to bend theshorting strip 31 to the contour of the hollowed indentation 35.

From the foregoing description it will be observed that there isprovided a centrifugal switch in which the desired electrical shortcircuit is obtained by the use of a narrow continuous strip of copperformed with a restricted frangible neck portion instead of relying upona conductive fluid to bridge the gap between two contacts. It will befurther observed that the mercury is initially contained within astainless steel cup out of contact with any copper or other metal partswhich have a strong tendency to amalgamate with the mercury, thusavoiding any possibility of contamination and the formation of sludgewhich might adversely affect the flow characteristics of the conductivefluid.

In the operation of the switch, the multiplicity of orifices formedbetween the roughened abutting surfaces 24 and 25 of the stainless steeldisks 22 and 23 are capable of preventing the passage of mercury atatmospheric pressure under the blows and impacts from normal handling asdescribed in my above mentioned application, but are capable of passingthe mercury in response to the centrifugal force set up by rotating theswitch 12 by means of the member 10. The resistance to the flow ofmercury from the annular groove 27 thence between the surfaces 24 and 25and out of the central hole 28 can be accurately controlled by varyingthe size of the grit if sand blasting is utilized to coarsen thesurfaces 24 and 25. By sand blasting the surfaces 24 and 25 to aroughness proportional to the required time delay in the flow of a givenvolume of mercury out of the inner cup 20 into the outer cup 30 throughthe multiplicity of orifices between these surfaces, it is possible toobtain time delays ranging from 0.1 second to 3.0 seconds under a givenpressure head.

The centrifugal unshorting switch 12 is positioned within the cavity 11with the closed end 36 of the outer cup 30 away from the axis ofrotation of the member 10. The pressure of centrifugal force acting uponthe light outer cup 30 is insufficient to cause the shorting strip 31 tobreak at the frangible portion 32 if no mercury has flowed into theouter cup 30. Nor will the frangible portion 32 rupture under impacts ofthe light outer cup 30 during normal handling. As the mercury flows intothe light outer cup 30 under spin conditions, the stress exerted againstthe frangible portion 32 granually increases, and when a volume ofmercury proportional to the required time delay has flowed into theouter cup 30, the pressure of centrifugal force acting against the outercup 30 is sufficient to break the shorting strip 31 at the frangibleportion 32. As described hereinbefore, the indentation 35 is hollowed toreceive the rounded closed end 36 of the outer cup 30 so that the brokenends of the shorting strip 31 are compressed by the outer cup 30 againstthe contour of the indentation 35 to move the broken ends further apartand prevent the re-establishment of a short circuit across the terminals13.

A positive short circuiting connection is thus provided through thecontinuous copper shorting strip 31 until sufi'icient mercury has flowedinto the outer cup 30 under the pressure of centrifugal force to rupturethe shorting strip 31 at the frangible portion 32. The mercury isinitially contained within a closed cup constructed entirely ofstainless steel and having no copper or other metal parts which have astrong tendency to amalgamate with the mercury. Thus any possibility ofa high resistance electrical short circuit occurring after a sufficientvolume of mercury has flowed through the restriction partition to openthe electrical circuit due to the deposition of film of an oxide ofmercury across the switch has been eliminated. Furthermore, theembodiment avoids the danger of erratic time delays due to contaminationand the formation of a sludge within the switch which might adverselyaffect the flow characteristics of the mercury.

While the embodiment of the present invention as herein describedconstitutes a preferred form, it is to be understood that other formsmight be adopted, all within the scope of the claims which follow. Itwill be evident to those skilled in the art that the use of a continuousshorting strip formed with a frangible portion could be applied totelescoped containers having a fibrous or sintered metal time delayelement sealed across the open end of the smaller container.

I claim:

l. A centrifugal unshorting switch comprising a pair of cup-shapedcontainers in telescoped sliding engagement with closed ends spacedapart and with the open end of the smaller of said containers adapted tobe sealed, time delay means sealed across the open end of the smallercontainer for retarding the flow of mercury out of the smaller into thelarger container, a body of mercury within the smaller container, ametal shorting strip formed with a frangible portion stretched across anindentation in front of the closed end of the larger container, saidfrangible portion being strong enough to withstand the impacts from saidlarger container due to blows and impacts occurring during normalhandling as well as the stress caused by centrifugal pressure exertedagainst said larger container before mercury has flowed into the largercontainer but weak enough to break under the stress caused bycentrifugal pressure exerted against said larger container after avolume of mercury proportional to the required time delay has flowedthrough said time delay means.

2. A centrifugal unshorting switch comprising a pair of cup-shapedcontainers in telescoped sliding engagement with closed ends spacedapart and with the open end of the smaller of said containers adapted tobe sealed, a pair of stainless steel disks sealed across the open end ofthe smaller container with the flat surfaces thereof abutting, one ofsaid disks having a central opening therein, the other disk having aplurality of apertures arranged in a circle concentric with said diskopening into an annular groove provided in the abutting surface thereof,at least one of the abutting surfaces being coarsened by sand blastingor etching to form a foraminous orifice between said surfaces whichallows passage of mercury under centrifugal pressure but preventspassage of mercury at atmospheric pressure under the blows and impactsoccurring during normal handling, a body of mercury within said smallercontainer, and a shorting strip of thin metal formed with a frangibleportion stretched across an indentation in front of the closed end ofthe larger container, said frangible portion being suificiently strongto Withstand the stresses caused by centrifugal force acting against thelarger container before mercury has flowed into the larger container andto withstand the stresses caused by the larger container hitting againstthe frangible portion under blows and impacts occurring during normalhandling but weak enough to break under the stresses caused bycentrifugal force acting against the larger con- 6 tainer after a volumeof mercury proportional to the required time delay has flowed throughsaid foraminous orifice into said larger container.

3. A centrifugal unshorting switch comprising a pair of cup-shapedcontainers in telescoped sliding engagement with the open end of thesmaller of said containers adapted to be sealed and enclosed within thelarger of said containers, a body of mercury within the smaller of saidcontainers adapted to flow into the larger of said containers and causeaxial movement thereof, means sealed across the open end of said smallercontainer for retarding the flow of mercury out of said smaller and intothe larger container, and a shorting strip of metal formed with afrangible portion stretched across an indentation in front of the closedend of the larger container and adapted to be engaged and broken bymotion of the larger container toward the indentation.

4. A centrifugal unshorting switch comprising a rotating member, a pairof open-ended containers in telescoped sliding engagement with the openend of the smaller of said containers adapted to be sealed and facingthe closed end of the larger container, said containers being mounted onsaid rotating member with the axis of said containers radial to the axisof rotation and with the closed end of the larger container away fromsaid axis of rotation, mercury within said smaller container, meanssealed across the open end of said smaller container for retarding theflow of mercury out of said smaller and into said larger container,centrifugal force acting on the mercury that flows into said largercontainer tending to cause axial movement thereof radially outward fromsaid axis of rotation, and a metallic shorting strip formed with afrangible portion mounted on said rotating member across an indentationin front of the closed end of the larger container and adapted to beengaged and broken by the radially outward movement of said largercontainer.

5. An unshorting switch, comprising a pair of openended containers intelescoped sliding engagement with the open end of the inner of saidcontainers adapted to be sealed and facing the closed end of the outercontainer, a body of mercury within said inner container adapted to flowinto said outer container and cause axial movement thereof, meanssealing the open end of said inner container, means associated with saidsealing means for controlling the flow of mercury from said inner intosaid outer container, and a rupturable conducting strip positioned inthe path of movement of said outer container and adapted to be engagedand broken thereby after a predetermined amount of mercury has flowedinto said outer container.

6. A centrifugal unshorting switch comprising a rotating member, a pairof open-ended containers in telescoped sliding engagement with the openend of the inner of said containers adapted to be sealed and facing theclosed end of the outer container, said containers being mounted on saidrotating member with the axis of said containers radial of the axis ofrotation and with the closed end of the outer container away from saidaxis of rotation, a body of mercury within said inner container, meanssealing the open end of said inner container, means associated with saidsealing means for controlling the flow of mercury from said inner intosaid outer container, the flow of mercury into said outer containercausing axial movement thereof, and a rupturable conducting strip onsaid rotating member positioned in the path of movement of said outercontainer and adapted to be engaged and broken thereby after apredetermined centrifugal force, due to the mercury within said outercontainer, is attained.

References Cited in the file of this patent UNITED STATES PATENTS

